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United States Patent |
5,594,396
|
Hino
|
January 14, 1997
|
Piezoelectric device including substantially parallel propagation paths
for secondary oscillations
Abstract
A piezoelectric device which has a piezoelectric substrate and a plurality
of piezoelectric resonators provided on the substrate. The piezoelectric
resonators are an energy-confining type, and when a voltage is impressed
on the piezoelectric resonators, each of the piezoelectric resonators
generates a primary vibration in a direction of the thickness of the
substrate and a secondary vibration in a direction on the surface of the
substrate. The secondary vibration, in the form of an oscillatory wave, is
propagated on the surface of the substrate and is attenuated gradually. At
least two of the piezoelectric resonators have propagation paths of
secondary vibrations which are substantially parallel to each other so as
not to intersect within the substrate.
Inventors:
|
Hino; Taketoshi (Nagaokakyo, JP)
|
Assignee:
|
Murata Manufacturing Co., Ltd. (JP)
|
Appl. No.:
|
393461 |
Filed:
|
February 23, 1995 |
Foreign Application Priority Data
| Feb 23, 1994[JP] | 6-025340 |
| Feb 23, 1994[JP] | 6-025341 |
Current U.S. Class: |
333/189; 333/185; 333/187 |
Intern'l Class: |
H03H 009/00 |
Field of Search: |
333/185-192
310/340
|
References Cited
U.S. Patent Documents
4196407 | Apr., 1980 | Masaie et al. | 333/191.
|
4234860 | Nov., 1980 | Schumacher et al. | 333/191.
|
4821004 | Apr., 1989 | Defranould et al. | 333/187.
|
Foreign Patent Documents |
58-11316 | Jan., 1983 | JP.
| |
0227417 | Oct., 1986 | JP.
| |
4026212 | Jan., 1992 | JP.
| |
Primary Examiner: Lee; Benny
Assistant Examiner: Gambino; Darius
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen, LLP
Claims
What is claimed is:
1. A piezoelectric device comprising:
a substantially rectangular piezoelectric substrate having a plurality of
peripheral edges; and
a plurality of piezoelectric resonators provided on the piezoelectric
substrate, each of the piezoelectric resonators including a plurality of
oscillation electrodes; wherein
at least two of the piezoelectric resonators are arranged on the
piezoelectric substrate to have propagation paths of vibration waves which
are slanted relative to the peripheral edge of the piezoelectric substrate
and are substantially parallel to each other.
2. A piezoelectric device as claimed in claim 1, wherein:
each of the plurality of piezoelectric resonators comprise energy-trap type
resonators.
3. A piezoelectric device as claimed in claim 1, further comprising:
a coupling capacitor which is electrically connected between two of the
piezoelectric resonators.
4. A piezoelectric device as claimed in claim 1, further comprising:
an armor which has internal cavities for containing the piezoelectric
resonators.
5. A piezoelectric device comprising:
a substantially rectangular piezoelectric substrate having a plurality of
peripheral edges; and
a plurality of piezoelectric resonators provided on the piezoelectric
substrate, each of the piezoelectric resonators including a plurality of
oscillation electrodes; wherein
at least two of the piezoelectric resonators are arranged on the
piezoelectric substrate to have propagation paths of vibration waves which
are propagated from the oscillation electrodes of the respective
piezoelectric resonators, the propagation paths being substantially
parallel to each other; and
at least one of the peripheral edges of the piezoelectric substrate has
slanted edge portions each of which is arranged to be slanted relative to
an adjacent one of the peripheral edges, each of the slanted edge portions
being located to intersect with a respective one of the propagation paths
of the vibration waves.
6. A piezoelectric device as claimed in claim 5, wherein:
each of the plurality of piezoelectric resonators comprise energy-trap type
resonators.
7. A piezoelectric device as claimed in claim 5, further comprising:
a coupling capacitor which is electrically connected between two of the
piezoelectric resonators.
8. A piezoelectric device as claimed in claim 5, wherein:
each of the propagation paths is substantially parallel to at least one of
the plurality of peripheral edges of the piezoelectric substrate.
9. A piezoelectric device comprising;
a substantially rectangular piezoelectric substrate having a plurality of
peripheral edges; and
a plurality of piezoelectric resonators provided on the piezoelectric
substrate, each of the piezoelectric resonators including a pair of
oscillation electrodes being separated from each other by a gap; wherein
each of at least two of the piezoelectric resonators are arranged on the
piezoelectric substrate to have a respective propagation path of vibration
waves which are propagated from an opening of the respective gap defined
by the respective pair of oscillation electrodes, the propagation paths
being slanted relative to the peripheral edges of the piezoelectric
substrate and being substantially parallel to each other.
10. A piezoelectric device as claimed in claim 9, wherein:
each of the plurality of piezoelectric resonators comprise energy-trap type
resonators.
11. A piezoelectric device as claimed in claim 9, further comprising:
a coupling capacitor which is electrically connected between two of the
piezoelectric resonators.
12. A piezoelectric device as claimed in claim 9, further comprising:
an armor which has internal cavities for containing the piezoelectric
resonators.
13. A piezoelectric device as claimed in claim 5, wherein the propagation
paths of the vibration waves are slanted relative to the peripheral edges
of the piezoelectric substrate.
14. A piezoelectric device comprising:
a piezoelectric substrate having a plurality of peripheral edges;
a plurality of piezoelectric resonators provided on the piezoelectric
substrate, each of the piezoelectric resonators including a plurality of
oscillation electrodes; wherein
at least two of the piezoelectric resonators are arranged on the
piezoelectric substrate to have propagation paths of vibration waves
propagating from the oscillation electrodes, the propagation paths being
substantially parallel to each other; and
at least one of the peripheral edges of the piezoelectric substrate having
a plurality of cutout portions located spaced from the oscillation
electrodes, each of the cutout portions being arranged to intersect with a
respective one of the propagation paths of the vibration waves.
15. The piezoelectric device of claim 14, wherein the propagation paths are
substantially parallel to at least one of the peripheral edges of the
piezoelectric substrate.
16. A piezoelectric device as claimed in claim 14, wherein:
each of the plurality of piezoelectric resonators comprise energy-trap type
resonators.
17. A piezoelectric device as claimed in claim 14, further comprising:
a coupling capacitor which is electrically connected between two of the
piezoelectric resonators.
18. A piezoelectric device as claimed in claim 14, further comprising:
an armor which has internal cavities for containing the piezoelectric
resonators.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric device, and more
particularly, to a piezoelectric device which has a plurality of
piezoelectric resonators.
2, Description of Related Art
Well-known piezoelectric devices include a type which has a piezoelectric
substrate supporting a plurality of piezoelectric resonators. In order to
reduce the size of this type of piezoelectric device, a piezoelectric
substrate of a smaller size must be used, and accordingly, the intervals
between the piezoelectric resonators become smaller.
When the piezoelectric resonators are disposed at short intervals,
interference is likely to occur among the resonators, thereby lowering the
spurious characteristic of the piezoelectric device. When a voltage is
supplied to the piezoelectric resonators, each of the piezoelectric
resonators generates a primary vibration in a direction of the thickness
of the piezoelectric substrate and also a secondary vibration in a
direction along the surface of the piezoelectric device. The secondary
vibration is propagated on the surface of the piezoelectric device in the
form of an oscillatory wave and is attenuated gradually. However, if the
intervals between the piezoelectric resonators are short, the secondary
vibration generated by one resonator reaches an adjacent resonator before
being attenuated sufficiently and interferes with the primary vibration
generated by the adjacent resonator. Thus, the piezoelectric device does
not have a good spurious characteristic
In the light of the problem, Japanese Utility Model Laid Open Publication
No. 58-11316 disclosed a piezoelectric device wherein two piezoelectric
resonators are arranged on a piezoelectric substrate such that secondary
vibrations generated by the respective resonators are propagated in
perpendicular directions which are at angles of about 45 degrees to the
peripheral edges of the piezoelectric substrate. This structure is to
prevent direct interference between the secondary vibrations of two
piezoelectric resonators by arranging the resonators out of the
propagation paths of the secondary vibrations generated by each other. In
the structure, however, the propagation paths of the secondary vibrations
of the two piezoelectric resonators intersect, and the secondary
vibrations interfere with each other at the intersection. Then, the
interference causes an undesired oscillatory wave, and the undesired
oscillatory wave interferes with the primary vibrations of the
piezoelectric resonators.
Because of the interference of the undesired wave with primary vibrations,
the structure to prevent the direct interference between secondary
vibrations is not so effective to improve the spurious characteristic as
might have been expected.
SUMMARY OF THE INVENTION
The preferred embodiments of the present invention provide to a
piezoelectric device which has no interferences among the piezoelectric
resonators and has a good spurious characteristic.
A piezoelectric device according to the preferred embodiments of the
present invention includes a plurality of piezoelectric resonators
disposed on a piezoelectric substrate, and oscillatory waves generated by
at least two of the piezoelectric resonators have propagation paths which
are substantially parallel to each other so as not to intersect within the
piezoelectric substrate.
The oscillatory waves are waves of secondary vibrations generated by the
piezoelectric resonators. In the structure, the propagation paths of the
secondary vibrations do not intersect, and the secondary vibrations do not
interfere with each other. Consequently, the secondary vibration of each
of the piezoelectric resonators do not interfere with a primary vibration
of the other piezoelectric resonator.
Another piezoelectric device according to the preferred embodiments of the
present invention comprises a plurality of piezoelectric resonators
disposed on a piezoelectric substrate, each of the piezoelectric
resonators including a plurality of oscillation electrodes, and
oscillatory waves generated from the oscillation electrodes of at least
two of the piezoelectric resonators have propagation paths which slant
with respect to the peripheral edges of the piezoelectric substrate and
are substantially parallel to each other so as not to intersect within the
piezoelectric substrate.
The oscillatory waves from the oscillation electrodes are waves of
secondary vibrations generated by the piezoelectric resonators. The
oscillatory waves of the secondary vibrations are propagated on the
surface of the piezoelectric substrate, and after they reach the
peripheral edges of the piezoelectric substrate, they are reflected
thereon and return to the respective piezoelectric resonators. In the
above structure, since the oscillatory waves of the secondary vibrations
are propagated at an incline or slant with respect to the peripheral edges
of the piezoelectric substrate, the oscillatory waves have long
propagation paths. Accordingly, the frequency of the secondary vibrations
is lowered, and the secondary vibrations of a low frequency do not
interfere with the primary vibrations of the piezoelectric resonators.
Further, since the propagation paths of the secondary vibrations do not
intersect, mutual interference between the secondary vibrations does not
occur, and consequently, an undesired oscillatory wave is not created by
the mutual interference between the secondary vibrations because no
undesired oscillatory wave is created by mutual interference between the
secondary vibrations, there is no possibility that an undesired
oscillatory wave interferes. with the primary vibrations of the
piezoelectric resonators.
Another piezoelectric device according to the preferred embodiments of the
present invention comprises a plurality of piezoelectric resonators
disposed on a piezoelectric substrate, each of the piezoelectric
resonators including a plurality of oscillation electrodes, and the
piezoelectric substrate has cutouts at locations which correspond to a
portion of the propagation paths of oscillatory waves generated from the
oscillation electrodes of at least two of the piezoelectric resonators.
Further, the propagation paths of the oscillatory waves are substantially
parallel to each other so as not to intersect within the piezoelectric
substrate.
In the structure described above, because of the cutouts, the oscillatory
waves, which are waves of secondary vibrations of the piezoelectric
resonators, have short propagation paths. Accordingly, the frequency of
the secondary vibrations is heightened, and the secondary vibrations
having a high frequency do not interfere with the primary vibrations of
the piezoelectric resonators. Also, because the propagation paths of the
secondary vibrations do not intersect, mutual interference between the
secondary vibrations does not occur, and there is no possibility that an
undesired oscillatory wave caused by the mutual interference between the
secondary vibrations may interfere with the primary vibrations of the
piezoelectric resonators.
Further, another piezoelectric device according to the preferred
embodiments of the present invention comprises a plurality of
piezoelectric resonators disposed on a piezoelectric substrate, each of
the piezoelectric resonators being formed by a plurality of oscillation
electrodes, and oscillatory waves of at least two of the piezoelectric
resonators which are generated from the respective gaps between the
oscillation electrodes have propagation paths which are substantially
parallel to each other so as not to intersect within the substrate.
The oscillatory waves generated from the gaps between the oscillation
electrodes are waves of secondary vibrations of the piezoelectric
resonators. The oscillatory waves are propagated on the surface of the
substrate. However, since the piezoelectric resonators are arranged out of
the propagation paths of the secondary vibrations of each other, the
secondary vibrations do not interfere with the primary vibrations of each
other. Further, since the propagation paths of the secondary vibrations do
not intersect, mutual interference between the secondary vibrations does
not occur, and there is no possibility that an undesired oscillatory wave
caused by the mutual interference between the secondary vibrations may
interfere with the primary vibrations of the piezoelectric resonators.
BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects and features of the preferred embodiments of the
present invention will be apparent from the following description with
reference to the accompanying drawings, in which:
FIG. 1 is a plan view of a piezoelectric substrate used in a piezoelectric
device which is a first preferred embodiment of the present invention;
FIG. 2 is a plan view of the piezoelectric device of preferred the first
embodiment;
FIG. 3 is an electric equivalent circuit diagram of the piezoelectric
device of FIG. 2;
FIG. 4 is a plan view of a piezoelectric substrate used in a piezoelectric
device which is a second preferred embodiment of the present invention;
FIG. 5 is a plan view of a piezoelectric substrate used in a piezoelectric
device which is a third preferred embodiment of the present invention;
FIG. 6 is a plan view of the piezoelectric device of the third preferred
embodiment;
FIG. 7 is an electric equivalent circuit diagram of the piezoelectric
device of the third preferred embodiment;
FIG. 8 is a plan view of a piezoelectric substrate used in a piezoelectric
device which is a fourth preferred embodiment of the present invention;
and
FIG. 9 is a plan view of a modified piezoelectric device of the second
preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Some preferred embodiments of the present invention are described with
reference to the accompanying drawings.
FIG. 1 shows a piezoelectric substrate 2, preferably used in a
piezoelectric device 1 which is a first preferred embodiment of the
present invention. On the piezoelectric substrate 2, two energy-trap type
piezoelectric resonators F1 and F2, and a coupling capacitor C1 are
provided. The piezoelectric substrate 2 preferably is a ceramic plate made
of Pb(ZrTi)O.sub.3, BaTiO.sub.3 a or the like.
The piezoelectric resonator F1 is located in the left portion of the
substrate 2 in FIG. 1 and comprises oscillation electrodes 4a and 4b which
are disposed on a side (the surface in FIG. 1) of the substrate 2 and an
oscillation electrode 4c which is disposed on the other side (the reverse
side in FIG. 1) of the substrate 2 so as to be opposite the electrodes 4a
and 4b. The piezoelectric resonator F2 is located in the right portion of
the substrate 2 and comprises oscillation electrodes 6a and 6b which are
disposed on the surface of the substrate 2 shown in FIG. 1 and an
oscillation electrode 6c which is disposed on the reverse side of the
substrate 2 so as to be opposite the electrodes 6a and 6c. The electrodes
4a and 6b are electrically connected to each other, and the electrodes 4c
and 6c are electrically connected to each other.
Numerals 15 and 16 denote propagation paths of secondary vibrations
generated by the piezoelectric resonators F1 and F2, respectively. These
propagation paths 15 and 16 are slanted or inclined relative to the
peripheral edges of the substrate 2 and are substantially parallel to each
other so that the paths 15 and 16 do not intersect within the substrate 2.
The coupling capacitor C1 is disposed in the center of the substrate 2 and
comprises capacitor electrodes 8a and 8b which are disposed on the
substrate surface shown in FIG. 1 and on the reverse side of the substrate
2, respectively, so as to be opposite each other. The capacitor electrode
8a is electrically connected to the oscillation electrodes 4a and 6b, and
the capacitor electrode 8b is electrically connected to the oscillation
electrodes 4c and 6c.
On the surface of the piezoelectric substrate 2, an input electrode 9 and
an output electrode 10 are disposed in the left portion and in the right
portion respectively.
Further, as shown in FIG. 2, an input terminal 11, an output terminal 12
and a common terminal 13 are preferably soldered to the input electrode 9,
the output electrode 10 and the capacitor electrode 8b, respectively.
Next, wax, paraffin or the like is preferably is coated over the
piezoelectric resonators F1 and F2. Thereafter, melted armor resin is
deposited on the piezoelectric substrate 2 by dipping or the like. Then,
the armor resin is hardened by heat, and simultaneously the wax or
paraffin fuses into the armor resin. Thus, the piezoelectric substrate 2
is housed in an armor 20 with the piezoelectric resonators F1 and F2
contained in cavities 21 and 22. A heat resisting and thermosetting resin,
such as epoxy resin, is preferably used as the material of the armor 20.
FIG. 3 shows the electric equivalent circuit of the piezoelectric device 1
of the above structure. The piezoelectric resonators F1 and F2 are
connected in parallel with the coupling capacitor C1 located therebetween.
The piezoelectric device 1 functions as a piezoelectric filter.
Next, referring to FIG. 1, advantages of the piezoelectric device 1 are
described.
When a voltage is supplied to the piezoelectric resonator F1 through the
input terminal 11, a primary vibration in a direction of the thickness of
the substrate 2 occurs between the oscillation electrodes 4a and 4b on the
face and the oscillation electrode 4c on the reverse side. Simultaneously,
the resonator F1 generates a secondary vibration in a direction on the
surface of the substrate 2. The secondary vibration, in the form of an
oscillatory wave, is propagated on the propagation path 15 from the
oscillation electrodes 4a and 4b. The oscillatory wave of the secondary
vibration is reflected on the peripheral edges of the substrate 2 and
returns to the piezoelectric resonator F1. The propagation path 15 is
slanted or inclined relative to the peripheral edges of the substrate 2
and accordingly obtains a large length, and thereby, the frequency of the
secondary vibration is lowered. Consequently, the secondary vibration
which returns to the piezoelectric resonator F1 does not interfere with
the primary vibration of the resonator F1. For the same reason, a
secondary vibration of the piezoelectric resonator F2 does not interfere
with a primary vibration thereof.
Further, since the propagation paths 15 and 16 do not intersect, mutual
interference between the secondary vibrations of the piezoelectric
resonators F1 and F2 does not occur, and there is no possibility that an
undesired oscillatory wave caused by the mutual interference between the
secondary vibrations may interfere with the primary vibrations of the
resonators F1 and F2.
Thus, the piezoelectric device 1 has no mutual interferences between the
piezoelectric resonators and has a good spurious characteristic.
FIG. 4 shows a piezoelectric substrate 32 used in a piezoelectric device
which is a second preferred embodiment of the present invention. On the
piezoelectric substrate 32, two energy-trap type piezoelectric resonators
F3 and F4, and a coupling capacitor C2 are provided. The piezoelectric
substrate 32 has cutouts 32a and 32b forming inclined edge portions on the
upper edge in the right and left portions viewed in FIG. 4.
The piezoelectric resonator F3 is located in the left portion of the
substrate 32 in FIG. 4 and comprises oscillation electrodes 34a and 34b
which are disposed on a side (the surface in FIG. 4) of the substrate 32
and an oscillation electrode 34c which is disposed on the other side (the
reverse side in FIG. 4) of the substrate 32 so as to be opposite the
electrodes 34a and 34b. The piezoelectric resonator F4 is located in the
right portion of the substrate 32 and comprises oscillation 36a and 36b
which are disposed on the surface of the substrate 32 and an oscillation
36c which is disposed on the reverse side of the substrate 32 so as to be
opposite the electrodes 36a and 36b. The electrodes 34a and 36a are
electrically connected to each other, and the electrodes 34c and 36c are
electrically connected to each other.
Numerals 45 and 46 denote propagation paths of secondary vibrations
generated by the piezoelectric resonators F4 and F5. The propagation paths
45 and 46 are parallel to the vertical (viewed in FIG. 4) edges of the
substrate 32 and do not intersect within the substrate 32. Because of the
cutouts 32a and 32b, the propagation paths 45 and 46 of the secondary
vibrations are shorter than those of a conventional piezoelectric device.
The coupling capacitor C2 is disposed in the center of the substrate 32 and
comprises capacitor electrodes 38a and 38b which are disposed on the
surface and on the reverse side respectively, so as to be disposed
opposite each other. The capacitor electrode 38a is electrically connected
to the oscillation electrodes 34a and 36a, and the capacitor electrode 38b
is electrically connected to the oscillation electrodes 34c and 36c.
On the surface of the piezoelectric substrate 32, an input electrode 39 and
an output electrode 40 are disposed in the left portion and in the right
portion respectively. The electrodes 39 and 40 are electrically connected
to the oscillation electrodes 34b and 36b, respectively.
Further, lead terminals are soldered to the capacitor electrode 38, the
input electrode 39 and the output electrode 40, respectively. Then, in the
same manner as described in the first preferred embodiment, the
piezoelectric substrate 32 is preferably housed in an armor with the
piezoelectric resonators F3 and F4 contained in cavities. The
piezoelectric device produced in this way functions as a piezoelectric
filter.
In the piezoelectric device of the above structure, a secondary vibration
generated by the piezoelectric resonator F3 is propagated on the
propagation path 45 in the form of an oscillatory wave. The propagation
path 45 is short because of the cutout 34a, and consequently, the
frequency of the secondary vibration is increased. Thereby, the secondary
vibration which returns to the resonator F3 does not interfere with a
primary vibration of the resonator F3. For the same reason, a secondary
vibration of the piezoelectric resonator F4 does not interfere with a
primary vibration of the resonator F4.
Further, because the propagation paths 45 and 46 do not intersect, mutual
interference between the secondary vibrations of the piezoelectric
resonators F3 and F4 does not occur, and there is no possibility that an
undesired oscillatory wave caused by the mutual interference between the
secondary vibrations may interfere with the primary vibrations of the
resonators F3 and F4.
Consequently, the piezoelectric device of the second preferred embodiment
has no mutual interferences between the piezoelectric resonators and has a
good spurious characteristic.
FIG. 5 shows a piezoelectric substrate 52 used in a piezoelectric device 51
which is a third preferred embodiment of the present invention. On the
piezoelectric substrate 52, two energy-trap type piezoelectric resonators
F5 and F6, and a coupling capacitor C3 are provided.
The piezoelectric resonator F5 is disposed in the left portion of the
substrate 52 in FIG. 5 and comprises oscillation electrodes 54a and 54b
which are disposed on a side (the surface in FIG. 5) of the substrate 52
and an oscillation electrode 54c which is disposed on the other side (the
reverse side in FIG. 5) of the substrate 52 so as to be disposed opposite
the electrodes 54a and 54b. The piezoelectric resonator F6 is disposed in
the right portion of the substrate 52 and comprises oscillation electrodes
56a and 56b which are disposed on the surface of the substrate 52 and an
oscillation electrode 56c which is disposed on the reverse side of the
substrate 52 so as to be opposite the electrodes 56a and 56b. The
electrodes 54a and 56b are electrically connected to each other, and the
electrode 54c and 56c are electrically connected to each other.
The piezoelectric resonator F5 has a gap 55 located between the oscillation
electrodes 54a and 54b, and the piezoelectric resonator F6 has a gap 57
between the oscillation electrodes 56a and 56b. The gaps 55 and 57 are
slanted or inclined relative to the peripheral edges of the substrate 52
and are parallel to each other. Numerals 65 and 66 which indicate paths
extending from the gaps 55 and 57 are propagation paths of secondary
vibrations of the resonators F5 and F6. The propagation paths 65 and 66
are substantially parallel to each other and do not intersect within the
substrate 52.
The coupling capacitor C3 located in the center of the substrate 52 and
comprises capacitor electrodes 58a and 58b which are disposed on the
substrate surface shown in FIG. 5 and the reverse side of the substrate
52, respectively, so as to be opposite each other. The capacitor electrode
58a is electrically connected to the oscillation electrodes 54a and 56b,
and the capacitor electrode 58b is electrically connected to the
oscillation electrodes 54c and 56c.
On the surface of the substrate 52, an input electrode 59 and an output
electrode 60 are disposed in the left portion and in the right portion
respectively. The electrodes 59 and 60 are electrically connected to the
oscillation electrodes 54b and 56a respectively.
Further, as shown in FIG. 6, an input terminal 61, an output terminal 62
and a common terminal 63 are preferably soldered to the input electrode
59, the output electrode 60 and the capacitor electrode 58b respectively.
Next, the piezoelectric substrate 52 is housed in an armor 70 with the
piezoelectric resonators F5 and F6 contained in cavities 71 and 72.
FIG. 7 shows the electric equivalent circuit of the piezoelectric device
51. The piezoelectric resonators F5 and F6 are connected in parallel with
the coupling capacitor C3 located therebetween. The piezoelectric device
51 functions as a piezoelectric filter.
Next, referring to FIG. 5, advantages of the piezoelectric device 51 are
described.
When a voltage is supplied to the piezoelectric resonator F5 through the
input terminal 61, a primary vibration in a direction of the thickness of
the substrate 52 occurs between the oscillation electrodes 54a and 54b on
the substrate surface, and the oscillation electrode 54c on the reverse
side. Simultaneously, the resonator F5 generates a secondary vibration in
a direction on the surface of the substrate 52. The secondary vibration,
in the form of an oscillatory wave, is propagated on the propagation path
65 from the gap 55. Since the other piezoelectric resonator F6 is located
outside of the propagation path 65, the secondary vibration of the
resonator F5 does not interfere with a primary vibration of the resonator
F6. Likewise, a secondary vibration of the piezoelectric resonator F6, in
the form of an oscillatory wave, is propagated on the propagation path 66
from the gap 57. Because the resonator F5 is located outside of the
propagation path 66, the secondary vibration of the resonator F6 does not
interfere with the primary vibration of the resonator F5.
Further, because the propagation paths 65 and 66 do not intersect, mutual
interference between the secondary vibrations of the piezoelectric
resonators F5 and F6 does not occur, and there is no possibility that an
undesired oscillatory wave caused by the mutual interference between the
secondary vibrations may interfere with the primary vibrations of the
resonators F5 and F6.
Consequently, the piezoelectric device 51 has no mutual interferences
between the piezoelectric resonators and has a good spurious
characteristic.
FIG. 8 shows a piezoelectric substrate 82 used in a piezoelectric device
which is a fourth preferred embodiment of the present invention. On the
piezoelectric device 82, two energy-trap type piezoelectric resonators F7
and F8, and a coupling capacitor C4 are provided.
The piezoelectric resonator F7 is located in the left portion of the
substrate 82 in FIG. 8 and comprises oscillation electrodes 84a and 84b
which are disposed on a side (the surface in FIG. 8) of the substrate 82
and an oscillation electrode 84c which is disposed on the other side (the
reverse side in FIG. 8) of the substrate 82 so as to be opposite the
electrodes 84a and 84b. The piezoelectric resonator F8 is located in the
right portion of the substrate 82 in FIG. 8 and comprises oscillation
electrodes 86a and 86b which are disposed on the surface of the substrate
82 and an oscillation electrode 86c which is disposed on the reverse side
of the substrate 82 so as to be opposite the electrodes 84a and 84b. The
oscillation electrodes 84a and 86a are electrically connected to each
other, and the oscillation electrodes 84c and 86c are electrically
connected to each other.
The piezoelectric resonator F7 has a gap 85 located between the oscillation
electrodes 84a and 84b, and the piezoelectric resonator F8 has a gap 87
located between the oscillation electrodes 86a and 86b. The gaps 85 and 87
are parallel to the horizontal (viewed in FIG. 8) edges of the substrate
82. Numerals 95 and 96 which indicate paths extended from the gaps 85 and
87 are propagation paths of secondary vibrations of the resonators F7 and
F8. The propagation paths 95 and 96 are parallel to each other and do not
intersect within the substrate 82.
The coupling capacitor C4 is located in the center of the substrate 82 and
comprises capacitor electrodes 88a and 88b which are disposed on the
substrate surface shown in FIG. 8 and on the reverse side of substrate 82
so as to be opposite each other. The capacitor electrode 88a is
electrically connected to the oscillation electrodes 84a and 86a, and the
capacitor electrode 88b is electrically connected to the oscillation
electrodes 84c and 86c.
On the surface of piezoelectric substrate 82, an input electrode 89 and an
output electrode 90 are provided in the left portion and in the right
portion respectively. The electrodes 89 and 90 are electrically connected
to the oscillation electrodes 84b and 86b, respectively.
Further, lead terminals are soldered to the capacitor electrode 88b, the
input electrode 89 and the output electrode 90. Then, the piezoelectric
substrate 82 is housed in an armor with the piezoelectric resonators F7
and F8 contained in cavities. The piezoelectric device which is produced
in this way functions as a piezoelectric filter.
The piezoelectric device of the fourth preferred embodiment has the same
advantages as the third preferred embodiment.
Piezoelectric resonators on a piezoelectric substrate may have any
configuration and layout. For example, when three piezoelectric resonators
are provided, it is not necessary that all the three resonators have
propagation paths of secondary vibrations which are slanted or inclined
relative to the edges of the substrate and are substantially parallel to
one another not to intersect within the substrate. What is necessary is
that any two of the three resonators have propagation paths of secondary
vibrations which meet the above conditions.
In the preferred second embodiment, the cutouts of the substrate may be of
any shape. As shown in FIG. 9, the substrate 32 may have cutouts 33a and
33b which are formed in the propagation paths 45 and 46. Further, the
propagation paths 45 and 46 do not have to be parallel to the vertical
edges of the substrate 32 and may be slanted or inclined relative to the
edges of the substrate 32.
Although the present invention has been described in connection with the
preferred embodiments above, it is to be noted that various changes and
modifications are possible to those who are skilled in the art. Such
changes and modifications are to be understood as being within the scope
of the present invention.
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